A diabetogenic gene (ODB-1) assigned to the X-chromosome in OLETF rats

Contribution of animal models to diabetes research: Its history, significance, and translation to humans

Diabetes mellitus is still expanding globally and is epidemic in developing countries. The combat of this plague has caused enormous economic and social burdens related to a lowered quality of life in people with diabetes. Despite recent significant improvements of life expectancy in patients with diabetes, there is still a need for efforts to elucidate the complexities and mechanisms of the disease processes to overcome this difficult disorder. To this end, the use of appropriate animal models in diabetes studies is invaluable for translation to humans and for the development of effective treatment. In this review, a variety of animal models of diabetes with spontaneous onset in particular will be introduced and discussed for their implication in diabetes research.

Insight into genetic, biological, and environmental determinants of sexual-dimorphism in type 2 diabetes and glucose-related traits

There is growing evidence that sex and gender differences play an important role in risk and pathophysiology of type 2 diabetes (T2D). Men develop T2D earlier than women, even though there is more obesity in young women than men. This difference in T2D prevalence is attenuated after the menopause. However, not all women are equally protected against T2D before the menopause, and gestational diabetes represents an important risk factor for future T2D. Biological mechanisms underlying sex and gender differences on T2D physiopathology are not yet fully understood. Sex hormones affect behavior and biological changes, and can have implications on lifestyle; thus, both sex-specific environmental and biological risk factors interact within a complex network to explain the differences in T2D risk and physiopathology in men and women. In addition, lifetime hormone fluctuations and body changes due to reproductive factors are generally more dramatic in women than men (ovarian cycle, pregnancy, and menopause). Progress in genetic studies and rodent models have significantly advanced our understanding of the biological pathways involved in the physiopathology of T2D. However, evidence of the sex-specific effects on genetic factors involved in T2D is still limited, and this gap of knowledge is even more important when investigating sex-specific differences during the life course. In this narrative review, we will focus on the current state of knowledge on the sex-specific effects of genetic factors associated with T2D over a lifetime, as well as the biological effects of these different hormonal stages on T2D risk. We will also discuss how biological insights from rodent models complement the genetic insights into the sex-dimorphism effects on T2D. Finally, we will suggest future directions to cover the knowledge gaps.

Subproteomic profiling from renal cortices in OLETF rats reveals mutations of multiple novel genes in diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a serious threat to human health, but its pathogenesis is not fully understood. Otsuka Long-Evans Tokushima Fatty (OLETF) rats are very similar to human DN in many aspects such as pathological changes and processes, and are deemed to be an ideal rodent model.

OBJECTIVE

This study was aimed to explore the pathogenesis of DN by analyzing the protein expression profile from renal cortices in OLETF rats.

METHODS

Thirty-six-week-old diabetic OLETF rats and normal control Long-Evans Tokushima Otsuka (LETO) rats were nephrectomized, and the renal cortices were isolated. The proteins were separated by soluble and insoluble high-resolution subproteomics methods for the analysis and identification of differential proteins.

RESULTS

Thirty-six differentially expressed proteins were found. Among them, 11 proteins had different isoelectric points and molecular weights between OLETF and LETO rats. Further sequencing identified point mutations in genes encoding eight of these proteins, which are involved in many biological processes closely related to DN, including oxidative stress and inflammation. Five of these eight proteins have not been reported in DN.

CONCLUSION

This study reveals mutations of multiple novel genes in diabetic OLETF rats, providing some new potential targets for the pathogenesis of DN and helping to better understand the pathogenesis of DN.

Reduced aldehyde dehydrogenase activity and arginine vasopressin receptor 2 expression in the kidneys of male TALLYHO/JngJ mice of prediabetic age

The TALLYHO/JngJ (TH) mouse is a novel polygenic model of type 2 diabetes and exhibits obesity, hyperglycemia (males), hyperinsulinemia, hyperlipidemia, and enlarged pancreatic islets. Since the kidney is damaged by hyperglycemia in other animal models, the present study aimed to determine the kidney phenotype of TH mice using immunoblot and histological analyses of the kidneys of 6-week-old (prediabetic) and 16-week-old TH mice. Interestingly, even 6-week-old male TH mice showed significant increases in kidney weight, compared to C57BL/B6 (B6) mice. Cuboidal parietal epithelium was observed in the Bowman's capsule in male TH mice at the prediabetic age. Water accumulated inside the kidneys of male TH mice in an age-dependent manner, but not in B6 mice. Since Swr/J mice are reported to develop diabetes insipidus and share 86.8% genotype homology with TH mice, the expression level of arginine vasopressin receptor 2 (AVPR2), a candidate protein for diabetes insipidus, was examined and determined to be significantly reduced in the kidneys of prediabetic male TH mice, compared to B6 mice. Aldehyde dehydrogenase (ALDH) activity in the kidneys of prediabetic male TH mice was significantly lower than that in age-matched male B6 mice, while there were no differences between female TH and B6 mice. These results suggest that the kidney phenotype of prediabetic TH mice occurs only in males, accompanied by a reduction in ALDH activity and AVPR2 expression. The kidney phenotype of male TH mice at a prediabetic age becomes evident before the onset of diabetes.

Sildenafil, a phosphodiesterase type 5 inhibitor, attenuates diabetic nephropathy in non-insulin-dependent Otsuka Long-Evans Tokushima Fatty rats

BACKGROUND

It is well established that the pathogenesis of diabetic nephropathy is associated with abnormalities of renal nitric oxide (NO) generation. Many of the biological actions of NO are mediated by cGMP, which is rapidly degraded by phosphodiesterases. In this study, we evaluated the renoprotective effects of sildenafil (SIL), an inhibitor of phosphodiesterase-5, in type 2 diabetic rats.

METHODS

Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a non-insulin-dependent diabetes model, and Long-Evans Tokushima Otsuka rats, a non-diabetic control, were treated with either SIL (2.5 mg·kg(-1) in drinking water) or undosed water for 28 weeks, starting at 30 weeks of age.

RESULTS

Sildenafil treatment significantly decreased albuminuria, attenuated glomerular hyperfiltration and resulted in a decrease in glomerular hypertrophy, in addition to a reduced glomerulosclerosis score and a dramatic decrease in the number of glomerular and tubulointerstitial proliferating cell nuclear antigen-positive cells in OLETF rats. This was accompanied by a significant reduction in renal cortical mRNA levels of collagen types I and III. The increased mRNA levels of matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitors of MMPs (TIMP)-1 and TIMP-2 in the OLETF rats were significantly or partially attenuated by SIL treatment.

CONCLUSIONS

This study suggests that SIL attenuated diabetic nephropathy due to its potent antiproliferative effects and its regulatory effects on extracellular matrix. This latter effect is thought to be a result of its ability to affect the balance between MMPs and their inhibitors.

The genetic landscape of type 2 diabetes in mice

Inbred mouse strains provide genetic diversity comparable to that of the human population. Like humans, mice have a wide range of diabetes-related phenotypes. The inbred mouse strains differ in the response of their critical physiological functions, such as insulin sensitivity, insulin secretion, beta-cell proliferation and survival, and fuel partitioning, to diet and obesity. Most of the critical genes underlying these differences have not been identified, although many loci have been mapped. The dramatic improvements in genomic and bioinformatics resources are accelerating the pace of gene discovery. This review describes how mouse genetics can be used to discover diabetes-related genes, summarizes how the mouse strains differ in their diabetes-related phenotypes, and describes several examples of how loci identified in the mouse may directly relate to human diabetes.

Urinary excretions of lipocalin-type prostaglandin D2 synthase predict the development of proteinuria and renal injury in OLETF rats

BACKGROUND

Otsuka Long-Evans Tokushima Fatty (OLETF) rats genetically develop diabetes which is associated with hypertension. In preliminary studies, urinary excretions of L-PGDS (lipocaline-type prostaglandin D synthase) increase before diabetic nephropathy obviously develops, and this may predict progression of renal injury following diabetes. In the present study, we attempted to define whether urinary excretions of L-PGDS behave as the predictor of development of diabetic nephropathy in OLETF rats.

METHODS

We investigated alterations of urinary L-PGDS excretions during the establishment of diabetes and assessed the relationship between the L-PGDS excretions and renal function in OLETF rats. Furthermore, we treated OLETF rats with troglitazone and analysed the effects on L-PGDS metabolisms. Urinary L-PGDS was measured by immunoenzyme assay and the occurrence of L-PGDS and its mRNA in the kidney was assessed by immunohistochemistry and a PCR method.

RESULTS

Urinary excretions of L-PGDS were significantly higher in OLETF rats than non-diabetic Long-Evans Tokushima Otsuka (LETO) rats. The excretions age-dependently increased in OLETF and this increase appeared to be due to increased glomerular permeability to L-PGDS. Messenger RNA and antigenicity of L-PGDS were demonstrated in renal tissue; however, the de novo synthesis of L-PGDS mRNA seemingly contributed to urinary L-PGDS excretions much less than glomerular filtration. Multiple regression analysis revealed that urinary L-PGDS was determined by urinary protein excretions, and not by high blood pressure per se. Conversely, urinary proteinuria in the established diabetic nephropathy was predicted by urinary L-PGDS excretions in the early stage of diabetes.

CONCLUSIONS

Urinary excretions of L-PGDS are likely to reflect the underlying increase in glomerular permeability. This property may be useful to predict forthcoming glomerular damage following diabetes in OLETF rats.

Abnormal renal structural alterations during the development of diabetes mellitus in Otsuka Long-Evans Tokushima Fatty rats*

AIM

The aim of this study was to investigate the renal structural properties in diabetic nephropathy.

METHODS

Flow-pressure and pressure-glomerular filtration rate (GFR) relationships were determined for maximally vasodilated kidneys at 10 (pre-diabetic stage) and 42 weeks of age (diabetic stage) in Otsuka Long-Evans Tokushima Fatty rats (OLETF), an animal model of type 2 diabetes mellitus, using age-matched Long-Evans Tokushima Otsuka rats (LETO) as non-diabetic controls (n = 9 of each age for each strain). Kidneys were then perfusion-fixed for histological analysis.

RESULTS

At 10 weeks of age, the slope of flow-pressure relationship (minimal renal vascular resistance, reflecting overall luminal dimensions of preglomerular and postglomerular vasculature) was steeper in OLETF than in LETO. In contrast, the threshold pressure for beginning filtration (preglomerular-to-postglomerular vascular resistance ratio) at pressure-GFR relationship did not differ between the two strains; however, the slope of the relationship (glomerular filtration capacity) was lower in OLETF than in LETO. Thus, in the kidneys of 10-week-old OLETF rats, vascular narrowing and impaired glomerular filtration capacity already existed with no abnormalities in preglomerular-to-postglomerular vascular resistance ratio. From the age of 10-42 weeks, the following results were obtained: (1) Minimal renal vascular resistance decreased in both strains, but it diminished markedly in OLETF. (2) The pressure for beginning filtration increased in LETO, but remained unchanged in OLETF. (3) Glomerular filtration capacity decreased to the similar extent in both strains. (4) Histologically, the vascular lumen and wall thickness increased in the interlobular arteries of both strains. However, vascular luminal widening was more pronounced in OLETF, resulting in the reduction in wall to lumen ratio. (5) Glomerular injuries and increased blood pressure occurred only in OLETF.

CONCLUSION

In conclusion, during progression from the prediabetic to diabetic stage of OLETF, the pre-existing vascular narrowing was markedly attenuated without the concomitant increase in preglomerular-to-postglomerular vascular resistance ratio. Combined with increased blood pressure, these renal structural alterations could lead to the elevation of intraglomerular pressure in OLETF.

Effect of pinealectomy on plasma levels of insulin and leptin and on hepatic lipids in type 2 diabetic rats

We previously reported that pharmacological melatonin administration to type 2 diabetic rats reduces hyperinsulinemia and improves the altered fatty-acid metabolism. To determine whether melatonin deficiency exacerbates diabetes-associated conditions, we investigated the effect of pinealectomy (i.e. melatonin-deficiency) on plasma hormone levels and lipid metabolism in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. We compared levels of insulin and leptin, and hepatic lipids in pinealectomized OLETF (PO) rats, sham-operated OLETF (SO) rats and sham-operated healthy Long-Evans Tokushima Otsuka (LETO) (SL) rats 16 and 30 wk after the operation. Plasma glucose and triglycerides were increased in SO and PO rats 30 wk after operation compared with age-matched SL rats. Pinealectomy caused an increase in free cholesterol among the plasma lipids, as compared with SO rats. Sixteen weeks after pinealectomy, typical hyperinsulinemia was observed in PO rats (3.47-fold increase, P < 0.01) as compared with SL rats, whereas at 30 wk, the plasma levels of insulin in PO and SO rats had decreased and there was no significant difference among the three groups. Hepatic triglycerides were increased (1.54-fold, P < 0.005) in PO rats, compared with SO rats. Hepatic acyl-CoA synthetase (ACS) activity was significantly augmented in PO rats at 30 wk (10%, P < 0.01 versus SO group), while microsomal triglyceride transfer protein (MTP) decreased (-27% versus SO, P < 0.05); thus, the increased ACS activity and decreased MTP might have a role in the accumulation of hepatic triglycerides in PO rats. In summary, pinealectomy causes severe hyperinsulinemia and accumulation of triglycerides in the liver, probably owing to the loss of the nocturnal melatonin surge.

Genetic analysis for diabetes in a new rat model of nonobese type 2 diabetes, Spontaneously Diabetic Torii rat

The Spontaneously Diabetic Torii (SDT) rat has recently been established as a new rat model of nonobese type 2 diabetes. In this study, we characterized diabetic features in SDT rats, and performed quantitative trait locus (QTL) analysis for glucose intolerance using 319 male (BNxSDT)xSDT backcrosses. Male SDT rats exhibited glucose intolerance at 20 weeks, and spontaneously developed diabetes with the incidence of 100% at 38 weeks, and glucose intolerance is well associated with the development of diabetes. The QTL analysis identified three highly significant QTLs (Gisdt1, Gisdt2, and Gisdt3) for glucose intolerance on rat chromosomes 1, 2, and X, respectively. The SDT allele for these QTLs significantly exacerbated glucose intolerance. Furthermore, synergistic interactions among these QTLs were detected. These findings indicate that diabetic features in SDT rats are inherited as polygenic traits and that SDT rats would provide insights into genetics of human type 2 diabetes.

Biochemical and morphological changes during development of sugar cataract in Otsuka Long-Evans Tokushima fatty (OLETF) rat

The relationship between the polyol pathway and sugar cataracts has been studied extensively using streptozotocin-induced diabetic rats and galactose fed rats as animal models for insulin-dependent diabetes mellitus (IDDM). In these models, sugar cataracts progress quickly, leading to rapid lenticular polyol accumulation in the early stages of cataract formation. In 1992, a new animal model of non-insulin-dependent diabetes mellitus (NIDDM), the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, was established. In the present study, we examined both biochemical and morphological changes in the lenses of the OLETF rats to determine whether these changes reflect those associated with diabetic cataract formation and to clarify their relationship with the polyol pathway. For the biochemical analysis, we measured the enzyme activity of aldose reductase (AR) and sorbitol dehydrogenase (SDH) and the sorbitol levels using 20, 40 and 60 week old OLETF or control Long-Evans Tokushima Otsuka (LETO) rats. Enzyme activities of AR and SDH, which were lower in 20 week old OLETF rats than in LETO rats, were increased in 60 week old OLETF rats. The lenticular sorbitol level of the OLETF rats was similar to the control level at 20 weeks of age, but it was markedly increased at 40 weeks of age, and slightly decreased at 60 weeks of age compared with rats at 40 weeks but not compared with controls. Slight lens fiber swelling was observed in the anterior and/or posterior subcapsular regions of 40 week old OLETF rats, accompanying elevated sorbitol level and slightly increased SDH activity in the lens. Swelling and liquefaction of lens fibers were observed in the subcapsular and supranuclear region of 60 week old OLETF rats, as well as decreased lenticular sorbitol, and markedly increased SDH activity compared with rats at 40 weeks. AR activity was also increased causing the elevation of sorbitol in lenses of OLETF rats during the early stages of cataract formation. Despite differences in the etiology of diabetes mellitus, the strain of rat and the rate of disease progression in the OLETF rat model compared with other diabetic models, the present results support the theory that the polyol pathway via AR is a factor in the development of sugar cataracts.

Genetic dissection of "OLETF," a rat model for non-insulin-dependent diabetes mellitus: quantitative trait locus analysis of (OLETF x BN) x OLETF

To identify genetic determinants relevant to non-insulin-dependent diabetes mellitus (NIDDM), we performed a genome-wide analysis for quantitative trait loci (QTLs) using 359 backcross progeny of the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. The OLETF strain is a well-studied animal model of obese NIDDM, with features of hyperinsulinemia, hyperglycemia, insulin resistance, and abundant abdominal fat. Our extensive genomic scanning with 218 markers revealed nine significant QTLs, including a strong determinant of obesity on chromosome 1 (Dmo1: LOD = 13.99, for body weight). Two highly significant QTLs for glucose homeostasis were found, one on chromosome 1 (Dmo4 LOD = 7.16, for postprandial glucose level) and the other on chromosome X (Dmo11/Odb1: LOD = 7.81, for postprandial glucose level). These data are comparable to results of our previous studies of the OLETF rat.

Genetic models for non insulin dependent diabetes mellitus in rodents

Efforts to identify human genes with major effects on insulin resistance and type II diabetes have yet to be successful because of the technical difficulties associated with the analysis of complex traits in humans. Animal models, particularly the rodent models with their well developed genetic tools, and their genetic similarity to humans, offer an alternate approach to access genes important in the etiology of diabetes. This approach is validated by the remarkable progress that has been made in the identification and characterization of the genes mutated in five monogenic mouse models of obesity. Identification of these genes has led to new insights into the etiology of obesity and provided promising targets for therapeutic intervention. Arguably, genetic animal models could do the same for our understanding of diabetes. In this brief review, we introduce rodent models of type II diabetes and report on the state of their genetic analyses.

Angiotensin-Converting Enzyme Inhibition Delays Onset of Glucosuria With Regression of Renal Injuries in Genetic Rat Model of Non-Insulin-Dependent Diabetes Mellitus

BACKGROUND: The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is a new genetic model of non-insulin-dependent diabetes mellitus (NIDDM). We investigated whether angiotensin inhibition influences the onset of NIDDM and brings about a regression of renal injury in diabetes mellitus. METHODS AND RESULTS: Six-week-old OLETF rats were treated with the angiotensin-converting enzyme (ACE) inhibitors imidapril or enalapril for 16 weeks. Systolic blood pressure is increased in an age-dependent manner in OLETF rats. In this study, the elevation in systolic blood pressure was dose-dependently reduced by ACE inhibitor treatment. In OLETF rats, plasma concentrations of insulin and glucose increased and the glucosuria occurred at the age of 22 weeks. Simultaneously, OLETF rats exhibited proteinuria and nodular lesions in glomeruli. The ACE inhibitor treatment almost completely reduced glucosuria, and also decreased plasma concentrations of insulin and glucose in OLETF rats. ACE inhibitor treatment lessened the proteinuria and attenuated morphologically the severity of nodular lesions in OLETF rats. Moreover, increases in plasminogen activator inhibitor 1 (PAI-1) in OLETF rats were reduced by the ACE inhibitor treatment, and the improvement of glomerular lesions was related to decreases of PAI-1 and angiotensin II levels in plasma but not to improvement of glucose metabolism. CONCLUSIONS: ACE inhibitors delay onset of NIDDM with attenuation of kidney injury. The regression of kidney lesions is probably due to angiotensin reductions but not to glucose metabolism per se. ACE inhibitor drug therapy may be useful in preventing NIDDM and the subsequent renal injury in patients with NIDDM.

X-linked locus is responsible for non-insulin-dependent diabetes mellitus in the OLETF rat

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat has been recently established as the best model of non-insulin-dependent diabetes mellitus (NIDDM) with mild obesity. In this study, we found that the F1 progeny produced from the crosses of OLETF and F344 rats exhibit a reciprocal cross effect on NIDDM-relevant phenotypes, fasting and postprandial glucose levels and body weight, suggesting the existence of X-linked locus affecting susceptibility to NIDDM. We thus examined the linkage between 7 X-linked microsatellite markers and NIDDM-relevant phenotypes, using 160 (OLETF x F344)F2 progeny. Suggestive evidence for a X-linked locus affecting glucose levels at 120 min after glucose administration was found in a region near X-linked marker, DXMgh4. The identified locus also showed significant effects on fasting glucose levels and body weight.

A disrupted cholecystokinin A receptor gene induces diabetes in obese rats synergistically with ODB1 gene

Otsuka Long-Evans Tokushima fatty (OLETF) rats develop hyperglycemia, hyperinsulinemia, and mild obesity, which are characteristic of human non-insulin-dependent diabetes mellitus. We have shown that two recessive genes, ODB1 mapped on the X chromosome and ODB2 mapped on chromosome 14, are involved in the induction of the diabetes in OLETF rats. Recently we found that OLETF rats are the naturally occurring cholecystokinin type A receptor (CCKAR) gene knockout rats. In this study, we focused on the genotype of CCKAR gene and the ODB1 gene in regulation of glucose homeostasis in the F2 cross of the OLETF rats. Relatively high plasma glucose levels were observed in the F2 offspring with the homozygously disrupted CCKAR gene. A synergistic effect for increasing plasma glucose levels in F2 rats between disrupted CCKAR gene and the ODB1 gene was shown. The CCKAR gene was found to map very close to ODB2 by a linkage analysis using microsatellite markers. These results suggest that CCKAR gene maintains normoglycemia in rats.

Genetic analysis of non-insulin-dependent diabetes mellitus in the Otsuka Long-Evans Tokushima Fatty rat

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model for obese NIDDM. We performed a genome wide scan in F2 progenies obtained by crossing OLETF rats with two control strains, Long-Evans Tokushima Otsuka (LETO) and Fisher-344(F-344) rats. Since diabetes develops only in male progenies, we used only male F2 rats for the linkage studies.Highly significant linkage was observed between the phenotype, postprandial hyperglycemia and P-450ald locus on chromosome 1 and D7Mit 11 locus on chromosome 7. In addition, suggestive linkage was found between fasting glucose level and body weight and these two loci. Four other regions (D1Mit12, D2Mit11, D5Mgh14, and D17Arb1) on chromosome 1, 2, 5, and 17 were detected to influence body weight, fasting glucose level or postprandial hyperglycemia independently. We concluded that non-insulin-dependent diabetes mellitus(NIDDM) in OLETF rats is regulated by multiple genes which affect fasting, postprandial hyperglycemia, and obesity differently.

Disrupted cholecystokinin type-A receptor (CCKAR) gene in OLETF rats

OLETF rats develop hyperglycemia, hyperinsulinemia and mild obesity, which is characteristic of human non-insulin-dependent diabetes mellitus (NIDDM). We cloned and sequenced the cholecystokinin type-A receptor (CCKAR) gene in the rats. Comparing the DNA sequences of the OLETF CCKAR gene and LETO CCKAR gene, normal gene, we found a deletion in the OLETF gene, 6847 bases in length, which was flanked by two 3-base-pair direct repeats (5'-TGT-3') at positions -2407/-2405 and 4441/4443, numbered according to the LETO gene sequence, one of which was lost. The promoter region, the first and second exons were missing in the mutant. The region upstream and downstream of the deletion, including exons 3, 4 and 5, was conserved between the two strains, and did not contain any base changes. We found that the gene mapped to chromosome 14 in rats. OLETF rats are the naturally occurring knockout animals with the homozygously disrupted CCKAR gene.

Obesity is necessary but not sufficient for the development of diabetes mellitus

To investigate whether inheritance or obesity plays a more important role in the development of non-insulin-dependent diabetes mellitus (NIDDM), female Otsuka-Long-Evans-Tokushima Fatty (OLETF) rats, which possess the diabetogenic gene, ODB-1, and Long-Evans-Tokushima-Otsuka (LETO) rats, which have no ODB-1, were compared. Neither strain becomes obese and diabetic when bred ordinarily. Female OLETF rats and male and female LETO rats were assigned to two groups of 20 rats each. Obesity was induced in one group by feeding a high-energy "cafeteria" diet (group D), and the other group was given standard chow (group C). Twenty male OLETF rats were used as NIDDM positive controls. At 25 weeks of age, the mean body weight of group D male LETO and female OLETF rats increased at a rate similar to that of male OLETF rats; female LETO rats did not show increased body weight. The incidence of diabetes mellitus in obese female OLETF rats in group D and positive control male OLETF rats was the same (80%). Only 30% of obese male LETO rats in group D developed diabetes mellitus. The insulin response to intravenous glucose in group D female OLETF rats was the highest for all groups but not sufficient to decrease blood glucose levels. In female OLETF rats, glucose infusion rate (GIR) during a euglycemic-hyperinsulinemic clamp test in group D was decreased to 50% of the group C value and tissue glucose uptake as determined by 3H-glucose infusion was significantly decreased in muscle. In male LETO rats, group D GIR was mildly decreased (80% of group C value) compared with the GIR of female OLETF rats. For obese group D female OLETF rats, abdominal fat increased more with obesity than in their male LETO counterparts. GIR was inversely correlated with the weight of abdominal fat when the data of all groups of animals were combined. The expression of GLUT4 mRNA and its protein level in adipose and muscle tissues and tumor necrosis factor alpha (TNF-alpha) protein in adipose tissue were not significantly different between group D and group C of both strains. In conclusion, the incidence of diabetes in female OLETF rats that possess the diabetogenic gene was significantly greater than in the LETO strains that do not possess the gene, in the presence of excess adiposity.

Relationships between diet control and the development of spontaneous type II diabetes and diabetic nephropathy in OLETF rats

The effect of a 30% restricted diet on the development of diabetes and diabetic nephropathy was examined using the Otsuka Long Evans Tokushima Fatty (OLETF) rat which develops non-insulin-dependent diabetes mellitus (NIDDM) spontaneously after 25-30 weeks of age. The first experimental group that received 30% restricted feeding from six to 80 weeks old, showed complete suppression of spontaneous diabetes up to 40 weeks of age and showed milder histopathological change of pancreatic islets, that those of the control group. The second group which received 30% restricted feeding during 30-80 weeks, showed a gradual decrease in clinical diabetes with age, even though they had already developed diabetes at 25 weeks. In both groups, levels of urinary protein content appeared to decrease, compared with that in control rats, although a gradual increase of urinary protein was observed with age. Histopathologically, glomerular damages were slight to mild in both groups. However, no improvement in nephrotic complication was observed for the group which received a 30% restricted feeding after 70 weeks of age. These results clearly show that the balanced-control diet, given at a 30% restricted feeding level and at an early phase, is effective in the prevention or improvement of NIDDM and nephrotic complications. Diet therapy after 70 weeks of age, however, had little or no effect.

Effects of obesity and inheritance on the development of non-insulin-dependent diabetes mellitus in Otsuka-Long-Evans-Tokushima fatty rats

We studied whether obesity or inheritance was the more important factor in the development of non-insulin-dependent diabetes mellitus (NIDDM) using female Otsuka-Long-Evans-Tokushima Fatty rats (OLETF) possessing one of the diabetic genes, ODB-1, and male Long-Evans-Tokushima-Otsuka rats (LETO) possessing no ODB-1, neither of which were diabetic when bred normally. Diabetes-resistant male LETO rats and female OLETF rats (4 weeks old) were assigned to three groups of 6 rats each, respectively; two groups in which obesity was induced by high calorie 'cafeteria' diet (D), or ventromedial hypothalamus lesions (V) with normal chow diet and a control group fed on normal chow (C). Six male OLETF rats were used as NIDDM positive controls. The mean daily energy intakes of obese male LETO and female OLETF rats were higher than those of the respective C groups. At 27 weeks of age, the average body weights of the obese LETO and female OLETF rats were significantly higher than those of the respective C groups and similar to that of the male OLETF group. Abdominal fat deposits of the obese groups were significantly higher than those of the respective C groups. At 28 weeks of age, the cumulative incidence of diabetes mellitus in obese LETO rats was 0% in group D and 17% in group V, while that of obese female OLETF rats in groups D and V were 100%. At 29 weeks of age, the plasma immunoreactive insulin (IRI) responses to glucose in obese female OLETF rats, groups D and V, were higher than that in group C. In obese LETO rats, insulin-stimulated glucose disposal in vivo was similar to that in group C, but in obese female OLETF rats, it was reduced to 41% in group D and 37% in group V of that in group C. Sections of islets of the pancreas of obese LETO rats appeared histologically normal, whereas those of obese female OLETF rats showed enlarged multilobulated fibrotic islets. These results demonstrate that obesity is necessary, but not sufficient alone for the development of NIDDM in these rat models.